I really can't get the hang of SSTO's

[Bishop149]

And I'm not sure why and and looking for advice.

I have built some that get to orbit, but I am starting to think its more by luck than good judgement.

I started encountering problems when I took one that worked and added enough parachutes to drop it safely. About 7-8 Mk2-R's were required adding 1-1.2 units of mass. . . . . aaaaand my SSTO plane didn't come close to making orbit any more.

So I bit the bullet and started looking for advice on what I was doing wrong.

I have watched a fair few tutorial vids and the big difference between my SSTO's and those I see seems to be the difference in my planes angle of attack and the horizon indicated by the yellow prograde marker. In most of the vids I have seen the two align most of the time. . . pitch up and the prograde marker pitches up to follow it closely in pretty short order.

Mine. . . doesn't.

This is pretty typical for me:

Pitched up by 20 degrees and only just about climbing. . . horizon at a few degrees above flat

That picture is taken pretty low and slow as well, it tends to get a bit more aligned as I go faster and higher . . up to a point and then it get much worse again. By the time I engage rockets I can pitch up 45 / 60 degrees and still barely be climbing. . . which leads me to think I wasting a ton of rocket fuel doing not very much.

I thought it may just be a case of not having enough lift. . . but I have stuck enough lifting surfaces on one of them to fly the bloody titanic and it makes no difference.

Another issue is the switch to rockets.

As soon as I switch to rockets (usually at around 28-30k up and 15-1700m/s over the ground) my speed starts to drop . . in order to maintain speed I have to ramp up throttle really high, which burns my fuel in short order leaving me well short of orbit. Again with all the vids I've seen it's a smooth transition at low throttle.

Another big difference between my planes and most of the tutorial ones is that mine are bigger (2 Turbojets, 1 LVT-45, about 900-1000 units of liquid fuel and less oxidiser is pretty standard) . . . . they need to be bigger to lift my payload, I tried on a tiny stripped back version and it just didn't cut it, didn't really get fast enough on jets and rockets were way too weedy.

Picture above is an intermediate version I tried. . . weedy rockets but two turbojets. . . . and yeah that one had annoying flame out = spin issues which I just couldn't manage.

So any tips? I am starting to feel I'm missing something big here!

Edited October 3, 2013 by Bishop149

[SpaceSphereOfDeath]

Daytime picture please?

[Bishop149]

Unfortunately all my testing last night on the smaller versions was. . . at night.

Here are some pictures of the planes that worked until I added the chutes, the latest versions have 8 RAM intakes instead of 6 and no radials, a few different lifting surfaces and the big tank is now half liquid fuel only . . oh and no split tail plane any more, those are bad!

[SpaceSphereOfDeath]

Unfortunately all my testing last night on the smaller versions was. . . at night.

Here are some pictures of the planes that worked until I added the chutes, the latest versions have 8 RAM intakes instead of 6, a few different lifting surfaces and the big tank is now half liquid fuel only . . oh and no split tail plane any more, those are bad!

MOAR wings is all I can say, I usually use a

Long wing

Delta. Structal

Wing. Wing. Arrangement.

[Richy teh space man]

Spamming air intakes will make your turbojets work at higher altitudes, you can use the debug console to place them on top of each other. I'm usually travelling at around 30k altitude at 2 km/s before firing up the rockets.

Also, remember to pay attention to the air intake on the resources tab, and throttle back when it starts to drop low.

[Gurrz]

Found a really good guide on reddit for SSTO's it's a very good beginners guide

http://www.reddit.com/r/KerbalSpaceProgram/comments/1izfqn/subs_planessto_design_for_beginners_long_post/

I think the problem you are having is that because the plane is so short you don't get a lot of leverage on your control surfaces making the craft easy to roll but hard to pitch. If you instead make the craft longer and narrower and put control surfaces as far away from the center of mass and lift as possible(think delta wing design with canards) you can get away with fewer control surfaces making the craft easier to pitch up and down and save on weight.

And don't worry to much about having enough wings for lift because usually the smaller SSTO's have a TWR quite a bit over 1 on the jet engines meaning you actually really don't need wings more than for control purposes.

Edited October 3, 2013 by Gurrz

[Bishop149]

Longer. . . hmmm honestly hadn't thought of that.

Also as it is my Center of Lift is behind my Center of Mass but it is only by the bearest of margins behind it.

I find if I move it back much more I can't lift the nose to get off the ground (ameliorated a bit by wheel positioning). . . . this may well fix that issue too.

Definitely worth a go! Cheers

Edited October 3, 2013 by Bishop149

[fatfluffycat]

You don't really need those big solar panels, could use the smaller ones for less mass

[arq]

From the moment you hit the rockets until you get your apo up to 70km (and actually a bit higher, 75-80, because of the drag you will hit going up), you should be burning full throttle. Anything less is just you losing more to gravity and drag. Also, you should be burning about 45deg above the horizon, at least until you get above 45km or so. The most important thing here is to get out of the thick part of the atmo.

As others suggested, larger lifting surfaces will reduce your 'angle of attack'. I'm a big fan of the Procedural Wings mod, which lets you make stock-balanced wings of arbitrary size.

More intakes will make it easier by letting you start higher (and, through reduced drag, faster), but at some point this makes it a joke. I usually aim for ~3 intakes per engine, but if you're really struggling you could try 5 or 6 per.

[katateochi]

I can hardly claim SSTO expertises, but I'd agree with what others are saying that you need more wings. If you have to keep your nose up to maintain a level flight then you don't have enough lift. Also I find control surfaces right at the front can be problematic. They may be the thing that gets your nose off the ground during take off, but once the fuel levels change you will find your COL shifts much further forward than your COM which can result in the plane pulling up hard and doing back flips or just generally being hard to control.

[Bishop149]

You don't really need those big solar panels, could use the smaller ones for less mass

Those are part of the payload.

This is the payload:

Smallest effective interplanetary craft I can build, its range is crazy . . . . . in fact the entire thing is crazy.

So I will try more wings and longer and report back!

[Rocket Farmer]

Very interesting rig you ahve.

So I'll add by 2 cents worth. I haven't watched any of the tutorials and only lightly read the forums before construction. I also play only stock and don't believe in part clipping at all. Needless to say I had many iterations before I got the SSTO that I wanted but I think you are looking for something similar.

The Elegent Albatross.

Width - 80% of width of the runway. Last time I looked I had 9 wheel assemblies under it to hold all the spans.

Mass - (I think I recall its around 150 some tonnes although I could be out a bit there as I haven't looked in awhile).

Jets - 6

Rockets - 2 Nukes, 2 L-30s and some 24-77s. I use all of them to boost out of the atmosphere and then just the nukes in orbit.

Changeover - At about 25,000m and 1300 m/s I turn off the last jets (start shutting them down at 21,000m) and kick on the rockets. Yes its low but without part clipping thats where I do it.

Claims to fame - It can deliver 3-4 tonne payloads landed at my Minmas base and then return to the kerbin base easy. Note without an atmosphere I land them tail first and then pitch forward at the last second which isn't for the faint of heart.

Search and rescue - Great for rescuing wayward kerbalnauts anywhere in the Kerbin SOI. It can easily be rigged to carry a couple of extra kerbalnauts.

Landing - I have a lot of lift on them and coming back near empty of fuel I usually just glide them in without any power. Works way better than I had expected. Before entering the atmosphere I usually transfer all the remaining fuel as far forward as possible to get my center of mass nice and even again.

Current attempts: Duna and return should be doable but so far the thin atmosphere and rocky terrain of Duna have made landing quite tricky.

Also I am thinking it should be able to make the run to my new Laythe base but my return will probably be by that electic motor only and I haven't had the time to try it yet.

My SSTO rules

1. At take-off if you can't pitch up and accelerate vertically it probably won't make it to space. I find this a good rule as while at low heights you have a lot of atmosphere to work with but when you get higher your machine has to be able to pitch up and down in much thinner air and you need a decent TWR to push your aircraft as fast as possible before switching to rockets.

2. Ensure your thrust is centered vertically on your mass. This seems simple but it wasn't for me. You will know something is wrong if as you climb higher your nose gets harder and harder to hold either up or down. What is occuring is that as the air thins your control surfaces aren't able to overcome the imbalance of your design. At a quick look this might be an issue for you. Remember you are not only designing a airplane for surface conditions but also for the much thinner air way up high.

3. Your Grampa flew in a bi-plane and so should you. I find 2-3 levels of wings can greatly enhance my ability to have lots of lift without requiring the strength to have a super wide airplane (again I am also almost at runway width so this is pretty much necessary to do it).

4. Bigger is better. Its nice that people build little space planes that get to orbit but they can't probably move more than 1 tonne up at a time and without part clipping / mods its very difficult to build them. I'm guessing you are like me and looking for something more useful that is able to deliver meaningful payloads into space. If so go big.

I also lose speed in the change-over to rocket power but its mostly because if I snap on all the rockets at once my wings tend to snap off so I have to feather the throttle in over 3-4 seconds from 0 - 100%. It doesn't seem to cause me much issue.

Lastly Personally I have never had much luck just using a nuke engine to push me into space. I would recommend some 24-77s. They aren't very efficient but they can give you that 30 second boost you need to clear the atmosphere much better than the nuke can and they don't up your mass much.

[Moar Boosters]

It might be an issue of thrust.

Why are you throttled back in the first picture? With spaceplanes faster = better. I can't see why you wouldn't run the engines full power.

Same with the change to rockets. If you don't want to run the rocket full power at least as the beginning of the rocket stage... you've picked too heavy a rocket, and should choose something lighter. An aerospike or the even an lv909 plus a few of the little orange radial ones would be more efficient than carrying the weight of an overpowered rocket engine.

[willy123]

It's a lack of thrust, in regards to weight. Need more thrust, but problem is, need more engines, more fuel, and thus more weight. Need to find a good balance. I find LESS is better. Check out the Ion Fighter SSTO on youtube. Dude gets into orbit with a single jet engine, ion engines, and solar panels. This is one of the few ways I, too, have gotten into orbit. With rocket engines MORE is needed, but that is a balance I have yet to master (though I have succeeded).

With less, like the Ion Fighter SSTO, you need to be getting to high velocities, >2km/s on jet alone, nearing the escape velocity of earth's atmosphere, nearly laterally. This will require getting high into the atmosphere (>28k) where there is less air resistance. This will require many ram air intakes, and a single engine to prevent loss of control from engine sputtering due to lack of oxygen. A single engine will require a light vehicle, which is no problem for an ion ssto, coupled with the jet engine and one fuel tank. Practice getting into that sweet spot of having barely enough oxygen and still be at full throttle, at the right altitude.

At this altitude, the solar panels can be opened without fear of them breaking off (due to less air resistance). Then the ion engines will provide just enough thrust while past the point where the jets can function to push the craft into orbit. You know you've done it when you are using only ion engines and the velocity is increasing (by 0.x km/s increments).

[Starglider]

Rocket Farmer is right about part clipping and small spaceplanes. I wanted a small spaceplane so I had to resort to that (I didn't go so far as needing to use the debug panel though). Some other comments from others that I've seen while doing my own "how to" research (I don't have names or http addresses to reference, so apologies to the posters - we really need one consolidated how to page with everything in it):

1) 1 jet engine per 10 tons of plane.

2) 3 intakes per engine. Even more is better. The ram air intake is the most efficient of the stock options available. You can place them without part-clipping using cubic octagonal struts and spacing them out along wings and fuselage (must face forward to be effective), but I find it more aesthetically appealing to clip them one-behind-the-other, in a column to each side of the main fuselage (if you do it right you don't need the debug panel).

3) Minimize your oxidizer to what you absolutely need, as rocket-style fuel tanks are heavy, and draw fuel from airplane fuselages (be aware the mk1 is less efficient than the mk2 in regards to fuel/weight). I'm going to put this into caps as it is all-important: WEIGHT IS NOT YOUR FRIEND! Trim everything you don't need. I once designed a plane that jettisoned the landing gear (with parachutes attached of course so they could be "recovered"), and relied on parachutes to "land" with, because each of the landing gear costs half a ton and the parachutes weighed so much less (that, and I wasn't "good" at landing on runways yet - more about that below).

4) This suggestion is all mine, based on what works for me (thus, YMMV) - wings generate lift, and you need enough lift to take off. However lift come from increasing drag. Having too much lift thus generates extra drag, which impedes your thrust potential. How much lift do you need? My rule of thumb, is that if you can't take off at less than 100 m/s, you need more lift, and if you can take off at less than 50 m/s, you may have too much lift. Some of my failed spaceplanes turned into successes just by removing some of the lifting surfaces.

5) Center of Mass must always stay in front of Center of Lift, but should still be as close as possible (you need it close so the plane stays responsive). This isn't as easy as just clicking the buttons and looking at the spots. As you use fuel and oxidizer, the center of mass changes. You have to figure out where the Center of Mass will end up at, as well as how it will shift in flight. Determine what percentage weight of fuel (meaning, total weight minus dry weight) is on each side of your initial CoM. You can add extra parts temporarily to the opposing side to simulate the mass balance with dry tanks. Once you know the final CoM position, work out how the CoM moves during flight. 99% of all spaceplanes drain fuel front-to-back, sending your CoM to the back of your plane before it eventually moves forward. I, however, represent the 1% (actually, I've never seen this recommendation online, anywhere, so this is another one from me) that disconnects the engines from the fuel columns (using that nice cubic octagonal strut) and runs fuel lines to the front of the fuel columns. In my planes, the fuel drains back-to-front, sending my CoM forward first; thus as long as my CoL is behind both my initial CoM and final CoM, I know I won't encounter stability issues.

6) Center of Thrust should be behind both CoM and CoL at all times.

7) Horizontal symmetry is vital. You can get away with a telescoping ladder on one side of the nose, but you will be able to see the difference in how the plane tries to yaw to the right. Anything more off-symmetry is asking for trouble. Vertical symmetry is almost as vital - your plane may flip over, in flight or in space, if you don't have this, but you can get away with some violations by using reaction wheels to compensate (but only up to a point, after which badness happens).

8) Odd numbers of jet engines are preferable, with the center jet engine placed last (more on this below). If you have an even number of jet engines, your spaceplane is automatically rated as "expert pilots only".

9) Start small. Get a spaceplane that has no cargo/docking/whatever capacity into orbit, before thinking about larger spaceplanes that can deliver cargo. When you go bigger, do it incrementally. So many more things can go wrong with spaceplane designs when compared to rockets.

10) Put your excess intakes into an action group, deactivate them on the runway, and reactivate them only when they are needed (at about 0.08 IntakeAir per engine) - this cuts down on drag.

11) Figure out how high you can go, yet still be able to pitch down into level flight at the slow horizontal velocity you have (you may need to revert several times while doing this "flight testing"). The question is basically, how much of the thick draggy air can you get out of, coming right off the runway? From there you can build up horizontal velocity and increase altitude further.

12) As IntakeAir drops under 0.08 per engine, you can throttle down proportionately. If you don't do it quite right, one engine will "flame out" - simply reduce your throttle until the engine reactivates, then increase again, but not to the previous level. It is the experience of other posters that the last engine to be placed, is the one that flames out first. Having your center engine placed last, thus helps it flame out first, eliminating any spinning issues resulting from this (provided you adjust before a second engine flames out, that is).

13) Before thinking of going into space, you should be able to hit 30km altitude and 2000m/s horizontal velocity.

14) It is my experience that my apoapsis is exceeding 125km altitude, and my periapsis is above 25km, before I worry about rockets at all (that's right, my "orbit" is almost entirely in place before I leave atmo). I don't tend to "pitch up" to get to space, so much as I "fly straight out of atmo". It is also my experience that its best to wait until I'm close to apogee before doing any rocket burns (even if not quite in space yet) - that oxidizer, being so heavy, is too precious to waste on increasing atmospheric drag through its use.

8) Use small rockets as most of your dV comes from your jets. I'd be overjoyed to see a 400+ Isp rocket with a thrust rating of 1-2 and a mass of less than 0.1 tons, but since I play 99% stock, I take what I can get (2xRockomax 24-77). I find I don't need the thrust ability of this rocket, but its weight is good, and I typically need more than an equivalent weight of LV-1Rs would produce (and the 24-77 has slightly better Isp).

9) Pointer for re-entry: if you aim to de-orbit your periapsis to about 35km, and do this on the opposite side of Kerbin to KSC, you will find yourself close to KSC when you're ready to land. You may need to tweak the altitude and burn-position based on your plane.

10) Pointer #1 for landing: construct a rover and place them directly east and west of the runway, at a distance of >500m. On your approach, you can target the nearest with your navball so as to line up early, and you can see them highlighted on your HUD, so you can keep them lined up vertically, and thus keep lined up with the runway (think of it as an "instrument landing system"). Be careful though - if you park the rovers too close, the game may want to clear them out before letting you take off.

11) Pointer #2 for landing: once you have your distance to the closest rover, add the distance to the runway, and divide the total by 10. That number should be your altitude. You should descend 100m per kilometer on your approach. This instantly tells you if you are too high or too low.

12) Pointer #3 for landing: use a flight-stick. Seriously. Keyboard airstrip landings are a nightmare, and a big reason I did parachute landings for awhile. Flight-sticks aren't exactly a dream (proper landings are difficult, even with the quasi-instrument-landing-system set up with #10 and #11), but waking up from a nightmare is still a major improvement.

13) This is one of my suggestions, as a private pilot: build and fly a small airplane first - not a spaceplane. Give it lots of fuel. Then, practice your landings. Land, take back off without stopping, circle around, and try it again. This is known as "touch and go". Get good at landings; the most stressful part of flying a spaceplane is landing at the very end, when you've done everything you set out to do, but that one last thing can screw everything up. You can't quicksave while moving in atmo; you'd have to reload from when you're in space (which probably means having to do your deorbit burn again too); and it takes time to get back to your landing attempt from space as you're limited to x4 physics warp (if your plane can handle even that). If you get impatient to do spaceplane launches, ditch the landing gear and descend on parachutes like I talked about earlier. It'll save you the headache.

That's all I can think of at the moment, but I probably forgot something somewhere. Time will tell.

[Starglider]

Oh yeah, Kerbil Engineer Redux is your friend. Its one of the few mods I use. I tried MechJeb but it was too laggy for me.

[Andrew Hansen]

I want to add to what willy123 said about the Ion Figher SSTO. I watched that video and was inspired to make my own SSTO. Behold, the JasperTech A-15!

(More pictures along with the .craft file can be found here).

It has 12 circular intakes on each side, two delta wings, six ion engines, two ant engines, and the OKTO2 and Mk1 Command pods as the control units. I'm new to KSP, so I'm sure my design isn't all that great, but it works!

In my quest to make a functioning SSTO, I've found a few things that seem to help. I would recommend you use landing legs and point your plane vertically for takeoff, since the landing legs are much lighter than wheels. The wheels are 0.5 kg each while the heavy-duty landing gear are only 0.1 kg.

Why take off vertically? Although this requires a thrust-to-weight ratio of above 1, I think that's great because it means you'll be able to get to higher speeds at higher altitudes using just your jet engines, which in turn means you'll have less delta V left for your rockets.

I take off, fly my plane to 25 km, then level off and start gaining speed. I basically just go as fast and as I as I can go, re-igniting my engine whenever I flame out. Then only when my intake is completely gone and I can't re-ignite, do I open my solar panels and turn on the engines. Once I get to above 50 km, I shut off the ant engines and the ion engines are enough to get me into orbit.

By the way, make sure to take off just before dawn so the ion engines work.

Good luck!

Edited October 6, 2013 by Andrew Hansen

[WafflesToo]

I'm not THAT experienced of a spaceplane designer but I'm confident in my ion-fu. My advice is to ditch the gigantors. They have less than half the power-to-mass ratio of the OX-4s. Build the probe long-and-thin and line them along the spine like sails. Your robot will have half-again the dV and your burn times will be shorter; a double win.

Don't worry about occlusion; the long 1x6 units have to be nearly on top of each other for it to happen.

Good luck sorting out the spaceplane.